Midterm 1:

Grade scale:

95% = 152	A = 4.0
90% = 144	A-= 3.7
85% = 136	B+ = 3.3
80% = 128	B=3.0
75% = 120	B-=2.7
70% = 112	C+ = 2.3
65% = 104	C = 2
60% = 96	C- = 1.7
55% = 88	D+ = 1.3
50% = 80	D = 1.0
45% = 72	< F

You may redo any problems you got wrong and resubmit them by

Monday March 20; you will get 1/3 of the extra points you earned added to

your test score.

Test Comments:

1. Given a function, how do you check whether it solves the DE or not?

2. Euler method: some confusion about how to get slope and then how to get y_new ?

3. Good

4. Good.

4d. Good aspects of model: its shows that the water in tub is decreasing and it is simple. Problem –

the model predicts an infinite time for tub to empty. Intuitively, we expect the tub to empty in a finite time.

More fine detail: does not take into account evaporation (perhaps not so important given length of time tub takes to drain).

Note that this problem is not discussing adding water to the tub.

5. Let $P(t)=$ amount of pollutant in the lake in kg. Some trouble with getting the correct term for dP/dt_out. Trouble getting the value of $P(0)$ .

Open book:

6c. Why is the fish population not sustainable if $C > 4 $ thousands. Just pointing out that there are no equilibrium points for C > 4 is not enough - maybe all P(t) go to +infinity if C > 4.